1. Field of Art
This invention relates to a vapor deposition reactor and a method for forming thin film on a substrate.
2. Description of the Related Art
Semiconductor materials include silicon-based semiconductors such as Si and SiGe, metal oxide semiconductors such as ZnO, group III-V compound semiconductors such as GaAs, GaP, GaN, AlGaAs and InP; and group II-VI compound semiconductors such as CdSe, CdTe, ZnS and CdHgTe. Semiconductor devices are manufactured using these as substrate material, forming metal films or insulating films on the substrate material, and carrying out processes such as photolithography, etching, cleaning and thin film deposition.
When fabricating a metal-oxide-semiconductor field-effect transistor (MOSFET) that is widely used in highly integrated circuits, an insulating film is formed on a semiconductor substrate. The insulating film is used as the gate insulating film for the transistor. Then, a metal film is formed on the substrate so that voltage or current required for driving the device can be applied. The reaction between the substrate and the metal film or the insulating film is important. In some cases, even a slight reaction may change properties of semiconductor devices. Therefore, a precise interface control is required to fabricate properly functioning semiconductor devices.
Deposition techniques associated with such fabrication processes are gradually shifting from chemical vapor deposition (CVD) such as low-pressure CVD (LPCVD) process (performed in a furnace) to atomic layer deposition (ALD) process. Generally, ALD process consists of four stages: (i) injection of a source precursor, (ii) removal of a physical adsorption layer, (iii) injection of a reactant precursor, and (iv) removal of a physical adsorption layer.
Because the source precursor is deposited on the semiconductor substrate after removing natural oxide films from the semiconductor substrate using HF or other chemical substances, the source precursor comes in direct contact with the semiconductor substrate. While the source precursor remains in contact with the substrate, mutual diffusion or formation of unwanted interface may occur on the surface of the semiconductor substrate due to the reaction between the substrate and the source precursor. In case the semiconductor device has a sufficiently large design rule, such phenomena has minimal effect on the properties of the semiconductor device. However, if the design rule is about 32 nm or smaller, as in nano devices or quantum devices, the reactions at the interface or the unwanted formation of interface may become relevant.
FIG. 1 is a flowchart illustrating ALD process according to a conventional technique. Referring to FIG. 1, ALD process may include: loading a substrate (S11), passing the substrate by a source precursor injection module to inject a source precursor (S12), passing the substrate by a purge/pumping module to remove a physical adsorption layer from the source precursor (S13), passing the substrate by a reactant precursor supply module to inject a reactant precursor (S14), and passing the substrate by a purge/pumping module to remove a physical adsorption layer from the reactant precursor (S15). The above steps may be repeated until a layer with desired final thickness is obtained (S16). To perform these steps, an expensive valve that sequentially supplies the source precursor, purge gas, reactant precursor, and a purge gas to the substrate is needed.
The reactors used for CVD generally inject a source gas from a showerhead type source injector that is located above the substrate. The reactors for ALD process may be classified largely into two types: (i) a cross-flow type (or travelling-wave type) that injects a reactant precursor and a purge gas in a direction parallel to the surface of the substrate, and (ii) a showerhead type that injects the reactant precursor and the purge gas in a direction perpendicular onto the surface of the substrate.
Korean Patent No. 10-0760428 discloses an example of a vapor deposition reactor for ALD. The vapor deposition reactor of the Korean Patent No. 10-0760428 is designed with a unit module capable of forming an atomic layer. The unit module includes an injection unit and an exhaust unit for a source material (which are collectively referred to as a source module), and an injection unit and an exhaust unit for a reactant (which are collectively referred to as a reactant module). The source module and the reactant module are disposed adjacent to each other.
With a plurality of unit modules, a plurality of atomic layers are obtained with each pass of the substrate across the unit modules. If the unit modules are disposed with certain intervals, chamber atmosphere may exist between the unit modules. The chamber is maintained in a vacuum state using a vacuum pump to remove the chamber atmosphere. As the size of the apparatus increases and more substrates are simultaneously loaded, the interior capacity of the chamber increases accordingly. The increased capacity in turn requires a higher-capacity vacuum pump to maintain the interior of the chamber in the vacuum state.